I need to move one side of a rod along a path but anchor the other side still
Blend file below...

The circular path -
Add the circle path and scale it to suit.  APPLY the scale with Ctrl+A
Bevel it when it has to be rendered.
In it's curve properties at right, set it's &quot;Frames&quot; to (e.g.) 20.
Set the timeline to frame 1 and in the curve's &quot;Evaluation&quot; slot, set that to zero and keyframe. (I)
Move the timeline to frame 20 and again in the path's evaluation slot, set that to 20 and keyframe.
Goto the Dopesheet and with the circle-path still selected, select both keyframes and press T --&gt; &quot;Linear&quot;.
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The path object - (empty)
Using the path's origin point, make sure the cursor is still set to that with SH-S.
Add an Empty.  Scale it to suit and 'APPLY' the scale with Ctrl+A .
Give it a &quot;Follow Path&quot; constraint.  Name the Curve-path as the 'Target'.
Play the animation and check the empty's travel is constant and is traveling around the curve properly.
Add a cube somewhere distant.
In Edit mode, select the vertical edge (corner edge) that's nearest the path.  Subdivide that with 'W'.
This will be the 'anchor point' for the rod.
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The rod -
Add a cylinder and scale it to suit. APPLY the scale with Ctrl+A.  Locate and rotate it roughly so it's pointing to both the path and cube.
Set it's origin point to the circle-path end so it will pivot from that end.
Give the rod a &quot;Track To&quot; constraint and name the cube as the target.
Enter the start &amp; end frames for the timeline as 1 to 20.
Play the animation and the rod should 'crank' around the circle, always pointing to the cube.
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When the rod must always be connected to the cube...
Add a hook at the rod's cube end and parent that to the cube.  (child = hook)  Drag the hook so they're connected.